Subprime-Car-Loan Firm Has Flourished as Other Lenders Have Struggled

Thomas Dundon's 13,556-square-foot Dallas home features eight bedrooms, indoor and outdoor tennis courts, three wet bars, a swimming pool and an indoor slide that goes from the second floor to the first.

Those are only some of the spoils Mr. Dundon, 42 years old, has collected during his journey to the top of the subprime auto-lending business,...